Post harvest diseases fruits and vegetables - Xavier University ...

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
Chemical Control 151
abundance of pathogenic spores, which may originate from infected
fruits and vegetables covered with spores, or from plant remnants in
the packinghouse or its surroundings, which serve as substrates for
many pathogenic fungi. During the citrus packing season, spores of
Penicillium digitatum and P. italicum form the most conspicuous
components of the spore population in packing houses and their vicinity.
Fruit containers, the equipment in the packinghouse, as well as the
workers' hands and tools, all bear pathogenic fungal spores during this
season. Fresh fruits arriving at the packinghouse may, therefore, come
into contact with pathogenic spores from any of these sources
(Barkai-Golan, 1966).
Many fruits and vegetables have to be cleaned and washed on arrival
at the packinghouse, in order to remove soil particles, dust or other
contaminants. Water that does not contain disinfectants becomes heavily
contaminated by fungal spores and bacterial cells and may infect
products treated with non-recirculated water. Chlorine is the principal
disinfectant used to sanitize wash water in packinghouses. Solutions of
hypochlorous acid and its salts (sodium or calcium hypochlorite) are the
most effective and economical agents available for destroying
microorganisms in water and they have been applied widely to reduce
bacterial contamination of the water used to wash or to hydrocool fruits
and vegetables (Eckert and Sommer, 1967). Elemental chlorine (CI2)
reacts with water to form hypochlorous acid (HOCI), hydrogen ion, and
chloride ion:
CI2+H2O '^—^ HOCl + C1-+H+
Hypochlorous acid is a weak acid (pka=7.46), which dissociates to
hypochlorite ion (OCl") and H+:
HOCl ^—^ 0C1-+H+
Hypochlorous acid and OCl" are in equilibrium in the solution, but the
antimicrobial effectiveness of the chlorine is correlated with the
concentration of the hypochlorous acid in the solution (Bartz and Eckert,
1987). The relative concentration of the hypochlorous acid and its
antimicrobial activity depend on the pH of the solution (Fig. 26).
If the initial concentration of hypochlorous acid is not sufficient to
kill microbes on contact, the hypochlorous acid formed by conversion
from hypochlorite ion should become involved, provided the exposure
period is long enough and the pH is not too high to inhibit the
http://arab2000.forumpro.fr